This invention is generally directed to novel squaraine compositions, and the incorporation of these compositions into layered photoresponsive devices. Thus, in one embodiment, the present invention envisions the use of novel squaraine compositions of matter as organic photoconductive materials in layered photoresponsive devices, especially those devices containing hole transport layers. In one important feature of the present invention, the sensitivity of the layered photoresponsive devices can be varied or enhanced allowing these devices to be capable of being responsive to visible light, and infrared illumination needed for laser printing. Accordingly, layered photoresponsive devices containing the novel squaraine compositions of the present invention can in one embodiment function so as to enhance or reduce the intrinsic properties of a charge carrier photogenerating material contained therein, in the infrared and/or visible region of the spectrum, thereby allowing these devices to be sensitive to either visible light, and/or infrared wavelengths. Moreover, there is provided in accordance with the present invention novel processes for preparing the squaraine compositions illustrated.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, or a composite layered device, containing a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described for example, in U.S. Pat. No. 3,121,006, wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The binder materials disclosed in this patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result, the photoconductive particles must be in a substantially contiguous particle-to-particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Thus, with the uniform dispersion of photoconductive particles described, a relatively high volume concentration of photoconductor material, about 50 percent by volume, is usually necessary in order to obtain sufficient photoconductor particle-to-particle contact for rapid discharge. This high photoconductive loading can result in destroying the physical continuity of the resinous binder, thus significantly reducing the mechanical properties thereof. Illustrative examples of specific binder materials disclosed in the '006 patent include, for example, polycarbonate resins, polyester resins, polyamide resins, and the like.
There are also known photoreceptor materials comprised of inorganic or organic materials wherein the charge carrier generating, and charge carrier transport functions, are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material. However, the art of xerography continues to advance and more stringent demands need to be met by the copying apparatus in order to increase performance standards, and to obtain higher quality images. Also, there is desired layered photoresponsive devices which are responsive to visible light, and/or infrared illumination needed for laser printing.
Recently, there have been disclosed other layered photoresponsive devices including those comprised of separate generating layers, and transport layers as described in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain diamines as mentioned herein. The disclosures of each of these patents, namely, U.S. Pat. Nos. 4,265,990 and 4,251,612, are totally incorporated herein by reference.
Many other patents are in existence describing photoresponsive devices including layered devices containing generating substances, such as U.S. Pat. No. 3,041,167, which discloses an overcoated imaging member containing a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying method by, for example, initially charging the member, with an electrostatic charge of a first polarity, and imagewise exposing to form an electrostatic latent image which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the imaging member can be charged with an electrostatic charge of a second polarity, which is opposite in polarity to the first polarity. Sufficient additional charges of the second polarity are applied so as to create across the member a net electrical field of the second polarity. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer such as by applying an electrical potential to the conductive substrate. The imaging potential which is developed to form the visible image, is present across the photoconductive layer and the overcoating layer.
There is also disclosed in Belgium Pat. No. 763,540, an electrophotographic member having at least two electrically operative layers, the first layer comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting the carriers into a continuous active layer containing an organic transporting material which is substantially non-absorbing in the spectral region of intended use, but which is active in that it allows the injection of photogenerated holes from the photoconductive layer and allows these holes to be transported through the active layer. Additionally, there is disclosed in U.S. Pat. No. 3,041,116, a photoconductive material containing a transparent plastic material overcoated on a layer of vitreous selenium contained on a substrate.
Furthermore, there is disclosed in U.S. Pat. Nos. 4,232,102 and 4,233,383, photoresponsive imaging members comprised of trigonal selenium doped with sodium carbonate, sodium selenite, and trigonal selenium doped with barium carbonate, and barium selenite or mixtures thereof.
Additionally, the use of certain squaraine pigments in photoresponsive imaging devices is known, reference, for example, the disclosure contained in a co-pending application wherein there is described an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer. As photoconductive compositions for this device there can be selected various squaraine pigments, including hydroxy squaraine compositions of the formula as outlined on page 13, beginning at line 21 of the co-pending application. Moreover, there is disclosed in U.S. Pat. No. 3,824,099, certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent the squaraine compositions are photosensitive in normal electrostatographic imaging systems.
Also, there is disclosed in another copending application. U.S. Ser. No. 493114/83, the disclosure of which is totally incorporated herein by reference, titled Photoconductive Devices Containing Novel Squaraine Compositions, photoresponsive devices containing novel squaraine compositions of matter, such as bis-9-(8-hydroxyjulolidinyl)squaraine. As disclosed in this copending application, one photoresponsive device is comprised of a supporting substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconducting composition layer capable of enhancing or reducing the intrinsic properties of the photogenerating layer, which composition is comprised of the novel squaraine materials disclosed in the copending application, and a hole transport layer. There is also illustrated in the copending application an improved photoresponsive device comprised of a substrate, a hole blocking layer, an optional adhesive or adhesion interface layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of a photogenerating layer in the infrared and/or visible range of the spectrum, which composition is comprised of the squaraine materials disclosed therein, an inorganic photogenerating layer, and a hole transport layer.
While photoresponsive devices containing the above-described squaraine compositions may be suitable for their intended purposes, there continues to be a need for the development of improved devices, particularly layered devices, containing other novel squaraine materials. Additionally, their continues to be a need for a development of a novel class of infrared squaraine photogenerating materials possessing desirable sensitivity, low dark decay, high charge acceptance values, and wherein devices containing such squaraines can be used for a number of imaging cycles in a xerographic imaging apparatus. Further, there continues to be a need for novel squaraine compositions which, when selected for layered photoresponsive imaging devices, allow the generation of acceptable images, and wherein such devices can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Moreover, there continues to be a need for improved layered imaging members wherein the materials selected for the respective layers are substantially inert to users of such devices. Furthermore, there continues to be a need for overcoated photoresponsive devices which are sensitive to a broad range of wavelengths, and more specifically are sensitive to infrared light, and visible light, thereby allowing such devices to be useful in a number of imaging and printing systems wherein lasers are selected, such as gallium arsenide aluminum lasers. Also, there continues to be a need for new squaraine compositions, and processes for preparing such compositions which are simple and economically attractive. There also continues to be a need for novel squaraine compositions which when incorporated into photoreceptor devices exhibit low dark decay, and wherein the squaraine compositions selected are capable of functioning with hole and electron transporting compounds.